The document discusses the key functions of the cardiovascular system. It explains that the heart is made of strong muscle that pumps blood from the atriums to the ventricles through small valves. The blood collected from the left side of the heart comes from the lungs and is bright red, while blood from the right side has carbon dioxide and is darker red as it is returned to the lungs. It also notes that the heart pumps blood throughout the body, which is essential for life.